The present invention concerns devices used for molding and for vulcanizing elastomeric material articles and especially, the presses used for vulcanizing vehicle-wheel tires.
Once any elastomeric material article is formed into a definite structure, it has to undergo a vulcanizing process --i.e. a thermal treatment, at a high temperature for a set duration, whereby the elastomeric material loses its characteristics of plasticity, and becomes transformed into an elastic material, provided with specific characteristics of mechanical resistance. In the particular instance of vehicle-wheel tires, the latter are enclosed inside a mold, then heated through conventional means known to technicians skilled in the art which thereupon, provides for the vulcanizing and the molding of the outer and inner surfaces of the tire. One problem of the heretofore used vulcanization processes is that of bringing the surfaces of the mold, which necessarily come into contact with the outer surface of the tire, to an adequate temperature and maintaining these surfaces at the specific temperature during the various working phases of the device including even during the opening cycles that are necessary for removing the vulcanized tire from the mold, and for re-loading a new, raw carcass into the mold for being vulcanized.
Included among the already known vulcanizing molds, there are the so-called centripetal-type molds that are necessary for vulcanizing radial tires. It is known that, in the crown zone, these tires are provided with an annular, reinforcing-structure that is circumferentially in-extensible, and which hence, does not allow for any expansion of the carcass when it is inside the vulcanizing mold. Therefore, for molding a tire and in particular, the tread pattern of the crown tread portion, it is necessary for the corresponding surface of the mold itself, to penetrate into the thickness of the tread-band. This is realized by working the mold surface, which corresponds to the outer perimeter surface of the tire, through a plurality of sectors that shift radially, in both directions, inwardly and outwardly. In such a manner the mold allows for the tire to be inserted therein, while the secotrs are in a radially expanded state. Next, the tread-band is molded through the radial, centripetal shifting of the sectors, and finally, the removal of the tire from the mold, through the further radial enlargement of the sectors.
It is clear that the problem of heating the surfaces in contact with the tire to be vulcanized, are not easily solved as far as the above-mentioned configurations are concerned, owing to the fact that the sectors thereof have to be shiftable (movable) with respect to the mold axis and reciprocally to each other. Various attempts have been made for solving this problem. One of the first methods used consists of enclosing the mold inside a further container, into which a high temperature vapor is introduced. The vapor evidently yields up its heat to the diverse parts of the mold which hence, reach the necessary temperature for the vulcanizing process. Among other considerations this system presents a serious disadvantage due to the fact that every time this container is opened for allowing the mold to be opened and the vulcanized tire to be removed, all of the vapor introduced will necessarily be discharged from the container and any residual part of the vapor, i.e. that which might still remain in the container, in fact will also disperse into the surrounding ambient, such that the parts which constitute the mold will undergo cooling. Therefore, when the container is once again closed, and another raw tire is introduced into the mold, a new quantity of vapor will have to be provided, and the parts of the mold, which in the meantime have cooled, will have to be once again brought back to the vulcanizing temperature required. This causes a noticeable lengthening of the vulcanizing cycle time, and a considerable dispersion or loss of heat.
For preventing this loss of precious energy, it is desirable to circulate the vapor inside the respective cavity provided in the supporting structure of the diverse mold parts and, in particular, in the containing-ring that guides the movement of the sectors. The disadvantage to be found in such a system is manifested by a reduction of the temperature between the containing-ring and the surface of the sector in contact with the tire which requires the ring to be raised to a decidedly higher temperature than what is generally specified for the vulcanizing process. In an effort to improve this procedure, attempts have been made to circulate the heating vapor inside a respective cavity circumscribed directly by the sectors. However, with this system there results a loss of vapor to the outside ambient each time that the mold is opened and sectors shift circumferentially and reciprocally one to the other. Hence, the very same drawbacks that are found in the device with the container previously described, are also experienced.